Silver particles are widely used in the manufacture of electrically conductive thick films for electronic devices and for other uses. Examples of thick film applications for silver particles include to make internal electrodes in multi-layer capacitors; interconnections in multi-chip components; conductive lines in auto defoggers/deicers, photovoltaic modules, resistors, inductors, antennas and membrane switches; electromagnetic shielding (such as in cellular telephones), thermally conductive films; light reflecting films; and conducting adhesives. A trend continues, however, to produce ever smaller particles for these and other applications. Generally, desirable features in such small particles include a small particle size; a narrow particle size distribution; a dense, spherical particle morphology; and a crystalline grain structure. Existing technology for manufacturing silver-containing particles could, however, be improved with respect to attaining all, or substantially all, of these desired features for particles used in thick film applications.
One method that has been used to make small particles is to precipitate the particles from a liquid medium. Such liquid precipitation techniques are often difficult to control to produce particles with the desired characteristics. It is especially difficult by the liquid precipitation route to obtain particles having dense, spherical particle morphology and with good crystallinity.
Aerosol methods have also been used to make small silver particles. One aerosol method for making small particles is spray pyrolysis, in which an aerosol spray is generated and then converted in a reactor to the desired particles. Spray pyrolysis systems involving silver have, however, been mostly experimental, and unsuitable for commercial particle production. Furthermore, control of particle size distribution is a concern with spray pyrolysis. Also, spray pyrolysis systems are often inefficient in the use of carrier gasses that suspend and carry liquid droplets of the aerosol. This inefficiency is a major consideration for commercial applications of spray pyrolysis systems.
There is a need for improved silver-containing powders, for improved methods of manufacturing silver-containing powders and for improved products incorporating or made using improved silver-containing powders.